XFCE suspend system command

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http://askubuntu.com – When I click on the exit icon there is a suspend option. When I click this the computer suspends, which works really well. I want to create a custom key mapping on the suspend command XK86Sleep (ThinkPad sleep button) which I can create using the keyboard settings. I have seen pm-suspend from numerous sources, but this requires root and so does not work. What command does XFCE use when pressing the Suspend option through the UI as described above? XFCE 4.8, Ubuntu 12.04, ThinkPad T60 (HowTos)